Art of recovering hydrocarbons



March 20, 1934. R. B. SMITH 1,951,885

ART OF RECOVERING' HYDROCARBONS Filed Oct. 26, 1931 I scrubbed GasMl'xfure 1 C/Iary ea bsorben f Medium INVENTOR lTead/fl B. 501/ #7Patented Mar. 20, 1934 UNITED STATES PATENT OFFICE I Reading BarlowSmith, Whiting, Ind., assignor to Sinclair Refining Company, New York,N. Y., a

corporation of Maine Application October 26, 1931, Serial No. 571,107

1' Claim.

This invention relates to improvements in the scrubbing of hydrocarbongas mixtures including a series of condensible hydrocarbon constituentsof progressively larger molecular weights, butane, 5 pentane and hexanefor example, to recover such condensible constituents from the gasmixture.

In conventional practice, an absorbent medium, frequently a hydrocarbonoil higher boiling than the hydrocarbon constituents to be recoveredfrom the gas mixture, is passed in countercurrent to the gas mixturethrough a series of zones, so called bubble trays in a tower forexample, in each of which the absorbent medium and the gas mixture arebrought into intimate contact, the raw gas mixture being introduced intothe zone through which the absorbent medium. last passes and thescrubbed gas mixture being discharged from the zone through which theabsorbent medium first passes.

As the gas mixture passes through successive zones, in such practice,the concentration of constituents of larger molecular weight, pentanefor example, decreases and that of constituents of smaller molecularweight, propane for example, increases. Constituents of smallermolecular weight are absorbed by the absorbent medium passing incountercurrent to the gas mixture in the zones through which the gasmixture last passes but are again displaced from the absorbent medium byconstituents of larger molecular weight in the zones through which thegas mixture first passes. The increase in concentration of constituentsof smaller molecular weight and the decrease in concentration ofconstituents of larger molecular weight in the gas mixture in the zonethrough which it first passes, and thereafter in the successive zones,is brought about by at.

least two factors, absorption of constituents of larger molecular weightand displacement of previously absorbed constituents of smallermolecular weight.

The absorbent medium leaving the zone through which it last passesapproaches equilibrium with the gas mixture leaving that zone, a gasmixture containing constituents of larger molecular weight inconcentration smaller than the concentration of these same constituentsin the raw gas mixture, instead of approaching equilibrium with the rawgas mixture. As a result, the absorbent medium is saturated with respectto the gas mixture leaving this zone but not with respect to the raw gasmixture entering this zone. In such conventional practice, it followsthat the absorptive capacity of the absorbent medium is never whollyutilized. This has been recognized by the use of a so called saturationfactor to bring calculations based on theoretical considerations, withrespect to design for example, into alignment with the observed facts.

In accordance with the present invention, the gas mixture leaving thefirst zone and entering the second zone, for example, is enriched withconstituents of larger molecular Weight to bring the absorbent mediumleaving the zone through which it last passes into equilibrium with agas mixture approximating the raw gas mixture in composition, or inother words into approximate equilibrium withv the raw gas mixture. Anumber of important advantages are thus secured. In one aspect theinvention increases the effective capacity of the absorbent medium to anextent such that the same net recovery from the same raw gas mixturepassing through the scrubbing operation at the same rate can beaccomplished with thesame absorbent medium circulating through thescrubbing operation at a rate decreased as much as 20% or more. Inanother aspect, the invention makes it possible to accomplish the samenet recovery with the same or a reduced rate of circulation of theabsorbent medium with a reduced number of zones in contact. Theseadvantages are reflected in reduced operating costs and in reducedequipment costs.

In accordance with the present invention, an absorbent medium is passedin countercurrent to the gas mixture through a series of zones in eachof which the absorbent medium and the gas mixture are brought intointimate contact, the scrubbed gas mixture is discharged from the zonethrough which the absorbent medium first passes, the raw gas mixture isdivided into two or more streams, one of these streams is introducedinto the zone through which the absorbent medium last passes, another ofthe streams is introduced into one of the preceding zones and otherstreams may be introduced into other preceding zones.

The invention will be further described in connection with theaccompanying drawing which illustrates, diagrammatically andconventionally, one form of apparatus adapted for the practice of theinvention. It will be understood that the invention can be practiced inother and diiierent forms of apparatus.

The accompanying drawing illustrates a scrubbing tower conventionalexcept for the provision of a manifolded group of connections 1a, 1b,1c, 1d and 1e between the connection 7 through which the raw gas mixtureis supplied and the five zones of contact through which the absorbentmedium last passes, 1, 2, 3, 4 and 5 respectively.

The zones of contact, the five just mentioned, the zone through'whichthe absorbent medium first passes 6, and the intermediate zones. mayconsist of conventional so called bubble trays. The absorbent medium issupplied through connection 8. The absorbent medium charged withabsorbed constituents is discharged through connection 9. The scrubbedgas mixture is discharged through connection 10.

In carrying out the invention in the scrubbing tower illustrated,instead of supplying all of the raw gas mixture supplied to the towerthrough a single connection corresponding to connection 1a, a part ofthe raw gas mixture is supplied through connection la, another part issupplied through connection 112,- and other parts may be suppliedthrough one or more of the connections 10, 1d and 1e. For example, 40%of the raw gas mixture may be supplied through connection la and 60%through connection 1b. Again for example, 40% of the raw gas mixture maybe supplied through connection la, 40% through connection 1b and 20%through connection 10. The concentration of constituents of largermolecular weight in the-gas mixture leaving the zone of contact 1 andentering the zone of contact 2 is thus increased by the addition of partof the raw gas mixture through connection 11). By thus adjusting thecomposition of the gas mixture leaving the zone through which theabsorbent medium last passes more closely to correspond to thecomposition of the raw gas mixture, the absorbent medium leaving thezone through which it last passes is brought into equilibrium with a gasmixture approximating the raw gas mixture in composition, or in otherwords into approximate equilibrium with the raw gas mixture. Byadjusting the composition of the gas mixture leaving the preceding zonein a similar manner, and so on, equilibrium with the raw gas mixture canbe approximated within substantially any chosen limit.

I claim:

In scrubbing hydrocarbon gas mixtures including a series of condensablehydrocarbon constituents of progressively larger molecular weights, theimprovement which comprises passing an absorbent medium countercurrentto the gas mixture through a series of zones in each of which theabsorbent medium and the gas mixture are brought into intimate contact,discharging the scrubbed gas mixture from the zone through which theabsorbent medium first passes, dividing the raw gas mixture into aplurality of streams and introducing said streams into the zone throughwhich the absorbent medium last passes and at least one of the precedingzones, thereby to bring the absorbent medium containing absorbedcondensable hydrocarbons leaving the zone through which the absorbentmedium last passes into approximate equilibrium with the raw gasmixture.

READING BARLOW SMITH.

